It is known to reduce the space required for elevator service in a building by providing more than one elevator car traveling in each elevator hoistway. If call assignments are limited and rudimentary, the avoidance of collisions between cars can be assured. However, such systems do not add significant service since many calls cannot be assigned. Examples are illustrated in U.S. Pat. Nos. 5,419,914, 6,360,849 and U.S. 2003/0164267.
In U.S. Pat. No. 5,877,462, elevator stop requests are processed to ensure that one car does not reach a stopping floor while another car will still be there, in accordance with a speed versus position profile applicable to both cars.
In order to cause the service achieved by several cars in one hoistway to approach the level of service which may be achieved by cars in several hoistways, it is necessary not only to assure that the cars will remain separated, but also permit the cars a maximal amount of movement in responding to calls for service.